Method of rendering clays filterable



Patented Dec. 28, 1943 METHOD 01F RENDELEHNG fiirdil'ffi FE'EERABLE No Drawing. Application @ctober 29, ion,

Serial No. amen (oi. Elli- 62) 2 Claims.

My present invention relates to the preparation of clays for use in the arts, particularly in the manufacture of certain ceramics and of coatings for papers, and provides a method by which alkaline clays may be rendered filterable.

Heretofore in the purification of kaolins it has been common practice to defiocculate the clay slip with such defiocculants as sodium silicate, sodium carbonate, ammonia, etc., and allow the coarse particles along with the impurities, such as fiint and feldspar, to settle out. After the coarse fraction has settled, the suspended clay is withdrawn from the tank. In this condition it has not been possible to filter slips as long as the water is alkaline because the clay particles are too small to be retained by the filter and therefore it has been customary to add a flocculant such as alum which produces settling of the clay and facilitates filtering.

I have discovered that alkaline slips, particularly thos made from or containing high gelforming clay such as hard Georgia kaolin, which have been defiocculated by means of sodium hy- Example A 5 kilograms of crude hard Georgia kaolin was dispersed in 25 kilograms of water by means of agitation and with the help of the addition or 25 grams of sodium hydroxide. Settling tests served to indicate the complete deflocculation of the clay. The settlings were removed and grams of 28% commercial acetic acid added to the sustrate is on the basic side of the neutral point.

Example B 5 kilograms of washed hard Georgia kaolin was dispersed in 25 kilograms of water by means of a high-speed stirrer, and the addition of 25 cc. of concentrated ammonia. 10 grams of sodium acetate were added and the slip heated to F. and placed in the pressure chamber of a small laboratory filter press. The air pressure was turned on and a clear' filtrate was obtained. The filtration was complete in seven hours. Without the presence or acetate ions and the application 01' heat, the filtrate would have been very turbid and the loss of material considerable. The filtration would have been impossible as far as the fine fraction of the clay is concerned. My improved process about halves the filtering time, and reduces the loss of material substan-- tially. Iclaim: 1. That step in the manufacture of alkaline deflocculated slips of kaolin or gel-forming clay minerals which comprises filtering the slips to which acetate ions have been added in amounts from 0.05 to 5 percent of the solids in the slips.

2. That step in the manufacture of alkaline defiocculated slips of kaolin or gel-forming clay minerals which includes in adding acetate ion forming materials in amounts from 0.05 to 5% of the solids in the slips,- and filtering the slips.

- FLEMMON P. HALL. 

